Conventionally, a communication system has been known which includes: a plurality of power consumption measuring instruments (hereinafter, also referred to as “taps”); a control device for collecting power information from the plurality of taps and controlling them; and an electronic device including a display. Each of the taps is connected to a receptacle in a house and measures an instantaneous power consumption of a household appliance connected to the tap. Further, each of the taps accumulates the instantaneous power consumptions to store an integrated power consumption. The electronic device including the display obtains the power information (the instantaneous power consumption and the integral power consumption) of each of the taps via the control device and is used to illustrate the power information of each tap in the form of a graph.
In such a communication system, a certain communication method is used to communicate between each tap and the control device. According to a general communication method, when starting to use each of the taps and the control device, a pairing process (or also referred to as “join process”) is necessary in order to allow each of the taps and the control device to be on the same network.
The pairing process is to allow a tap to participate in the network of the control device. The network of the control device means a network formed by the control device or a network in which the control unit is currently participating. Participating in a network is also referred to as “joining”.
Upon performing the pairing process, the tap to join stores information (hereinafter, referred to as “network information”) about the network of the control device. In addition, the control device stores information (hereinafter, referred to as “device information”) about the tap. Here, the storing is also referred to as “registering”.
Generally, these information are stored in nonvolatile memories of both the tap and the control device. Hence, once the pairing process is over, the information will not be lost even when the power source is turned off. Therefore, the pairing process is performed only once upon starting the use thereof.
Moreover, generally, the pairing process is usually performed in accordance with a user. Some types of products are through such a pairing process between a control device and a plurality of taps in factory before shipment. However, in order to add a tap at a later point of time or the like, it can be said that the pairing process performed in accordance with the user is substantially essential. In doing so, the method for pairing process should be as simple as possible such that anyone can perform the pairing process.
In some communication methods, the control device is configured not to store the information (device information) about the tap. However, in the present invention, it is assumed that the control device stores the information (device information) about the tap.
Meanwhile, a leave process is an operation contrary to the pairing process. The leave process is to withdraw the tap from the network of the control device. The withdrawal from the network is also referred to as “leaving”. When the leave process is performed, the tap to leave deletes the network information stored in the tap. Moreover, the control device deletes the information (device information) about the tap stored in the control device.
To summarize, when starting the use of the tap, the tap needs to join the network formed by the control device. Moreover, when ending the use of the tap, the tap needs to leave from the network formed by the control device.
The leave process is necessary because the following inconveniences would otherwise arise.
Inconvenience (1): If an unused tap is not left and is kept on the network, the control device assumes that the tap exists thereon, and attempts to continue communication with the tap. When the tap is disconnected from the receptacle, the communication cannot be made. However, the control device cannot precisely determine whether or not the tap is disconnected from the receptacle. Accordingly, some communication with the tap will continue. This results in occurrence of unnecessary and wasteful traffic on the network.
Inconvenience (2): If an unused tap is not left and is kept on the network, the tap may continue to transmit some packets to the network when the tap is connected to the receptacle. This also results in occurrence of unnecessary and wasteful traffic on the network.
Inconvenience (3): In the case where an upper limit is set as to the number of devices registerable in the control device, the upper limit is practically reduced by one in number. Because there is a limit in the number of registerable devices, the device information of an unused tap should be deleted from the control device.
Inconvenience (4): If an unused tap is lost and a third party obtains the tap, the third party may be able to monitor communication using the tap. Because the tap has the network information stored therein, the tap is capable of communicating with other devices on the network. This is not good in terms of security.
Further, for the leave process, the registered information should be deleted from both the tap to leave and the control unit in conjunction with the tap and the control device. If they are not in conjunction with each other, the registered information may be deleted from one of them but may not be deleted from the other. Specifically, the following two cases may take place.
Case (1): The network information is deleted from the tap to leave. However, the device information about the tap is not deleted from the control device. In this case, the above-described inconvenience (1) and inconvenience (3) may take place.
Case (2): The device information about the tap is deleted from the control device. However, the network information is not deleted from the tap to leave. In this case, the above-described inconvenience (2) and inconvenience (4) may take place.
Non-Patent Document 1 discloses a leave process in the ZigBee® specification. This specification indicates a method of participating in a ZigBee network and a method of withdrawing therefrom.
Here, the leave process in the ZigBee specification will be described.
Here, for the purpose of explanation, the device forming the network will be referred to as a “parent node”. A device participating in the network of the parent node will be referred to as a “child node”. The leave process is performed in two manners depending on whether the leave process is started by the parent node or the child node. A node to start the leave process is also referred to as an “initiator”.
(1) Case where Child Node Starts Leave Process:
When the initiator is the child node, the child node provides a notification, through broadcasting, that the child node is leaving (withdrawing) from the network.
Specifically, the child node provides a NLME-LEAVE.request(DeviceAddress=NULL), which is a leave command, through broadcasting for the purpose of notification.
When the other nodes receive this, the other nodes delete the information about the node to leave, from its adjacent table or other internal data structures (Non-Patent Document 1: 3.6.1.10.3 Upon Receipt of the Leave Command Frame).
However, the child node having withdrawn does not delete the network information. The child node having withdrawn is only temporarily brought into a hold state (state in which it does not participate in the network after being reset).
Therefore, for example, when the child node is powered on again, the child node can participate in the network held in the child node again.
(2) Case where Parent Node Starts Leave Process (with Child Node being Designated):
When the initiator is the parent node, the parent node designates a child node to leave and requests it to leave.
Specifically, through unicasting, the parent node notifies the child node to leave by means of a NLME-LEAVE.request(DeviceAddress=NonNULL), which is a leave command.
When the child node receives this, the child node is temporarily brought into the hold state (state in which it does not participate in the network after being reset) but does not delete the network information. According to a certain implementation, the child node is brought into the hold state 5 seconds after receiving it. On the other hand, the parent node deletes the information about the child node to leave, from its adjacent table or other internal data structures (Non-Patent Document 1: 3.6.1.10.2 Method for a Device to Remove Its Child from the Network).
Thus, even through the child node is withdrawn from the network, the network information or the like is maintained in the child node. Therefore, for example, when the child node is powered on again, the child node can participate in the network held in the child node.
In the meanwhile, according to another conventional technique, by pressing a button of a tap for a long time, network information is deleted from the tap or the tap is initialized (to the factory settings).
Regarding this point, Non-Patent Document 2 shows a method of canceling registration of a PLC adapter, for example.
Specifically, Non-Patent Document 2 shows an operation of pressing a setting button of the PLC adapter for a long time, specifically, 10 seconds or longer. With this operation, the information set in the PLC adapter can be initialized (to the factory settings).